Visually controlled photoconductographic process



9, 1966 F. URBACH I 3,265,595

VISUALLY CONTROLLED PHOTOGONDUCTOGRAPHIC PROCESS iled 001;. 25, 1960 Franz Urbach INVENTOR.

United States Patent Filed Get. 25, 1960, S61. No. 64,901 1 Claim. c1. 20418) This invention relates to photoconductography. Photoconduct-ography forms a complete image at one time or at least a non-uniform part of an image as distinguished from facsimile which at any one moment produces only a uniform dot. The present invention is applicable to all forms of photoconductography.

Cross reference is made to the following series of applications filed July 28, 1960:

Serial No. 45,940, John W. Castle, Jr., Photoconductography Employing Reducing Agents, now Patent No. 3,227,076.

Serial No. 45,941, Raymond F. Reithel, Photoconductolithography Employing Nickel Salts, now abandoned, now continua'tion-in-part Serial No. 120,863, filed June 7, 1961, now Patent No. 3,106,157.

Serial No. 45,942, Raymond F. Reithel, Photoconductolithography Employing Magnesium Salts, now US. Patent 3,033,179.

Serial No. 45,943, Raymond F. Reithel, Photoconductography Employing Spongy Hydroxide Images, now abandoned, now continuation-in-part Serial No. 120,035, filed June 27, 1961, now Patent No. 3,106,518.

Serial No. 45,944, Raymond F. Reithel, Method for Making Transfer Prints Using a Photoconductograpliic Process.

Serial No. 45,945, Raymond F. Reithel, Photoconductography Employing Manganese Compounds, now abandoned.

Serial No. 45,946, Raymond F. Reithel, Photoconductography Employing Molybdenum or Ferrous Oxide, now abandoned, now continuation-in-part Serial No. 120,036, filed June 27, 1961, now Patent No. 3,106,156.

Serial No. 45,947, Raymond F. Reithel, Photoconductography Employing Cobaltous or Nickelous Hydroxide, now abandoned, now continuation-in-part Serial No. 120,037, filed June 27, 1961, now US. Patent 3,057,- 788.

Serial No. 45,948, Donald R. Eastman, Electrophotolithography.

Serial-No. 45,949, Donald R. Eastman, Photoconductolithography Employing Hydrophobic Images, now Patent No. 3,152,969.

SerialNo. 45,950, Donald R. Eastman and Raymond F. Reithel, Photoconductography Employing Electrolytic Images to Harden or Soften Films, now abandoned.

Serial No. 45,951, Donald R. Eastman and Raymond F. Reithel, Photoconductography Employing Absorbed Metal Ions, now abandoned, now continuation-in-par-t Serial No. 120,038, filed June 27, 1961.

Serial No. 45,952, Donald R. Eastman and Raymond F. Reithel, Photoconductography Employing Spongy Images Containing Gelatin Hardeners, now Patent No. 3,028,147.

Serial No. 45,953, John J. Sagura, Photoconductography Employing Alkaline Dye Formation, now U.S. Patent 3,057,787.

Serial No. 45,954, John J. Sagura and James A. Van Allan, Photoconductography Employing Quaternary Salts, now Patent No. 3,178,362.

Serial No. 45,955, Franz Urbach and Nelson R. Nail, Uniform Photoconductographic Recording on Flexible Sheets, now abandoned.

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Serial No. 45,956, Franz Urbach and Nelson R. Nail, High Contrast Photoconductographic Recording, now abandoned.

Serial No. 45,957, Nicholas L. Weeks, Photoconductography involving Transfer of Gelatin, now Patent No. 3,103,875.

Serial No. 45,958, Donald R. Eastman, Photocondutolithography Employing Rubeanates, now Patent No. 3,095,808.

Serial No. 45,959, Donald R. Eastman and Raymond F. Reithel, Electrolytic Recording with Organic Polymers, now Patent No. 3,106,155.

Serial No. 46,034, Franz Urbach and Donald Pearlman, Electrolytic Recording, now abandoned.

Cross reference is also made to the following copending applications: Serial No. 64,902, Urbach and Nail, and Serial No. 64,903, Urbach, now Patent No. 3,194,748, both filed concurrently herewith.

Photoconductograp-hy is described in detail in British 188,030 Von Bronk and British 464,112 Goldmann, modifications being described in British 789,309 Berchtold and Belgium 561,403 Johnson et al.

The present invention is not concerned with those processes in which the development occurs entirely after the exposure of the photoconductive layer has been completed. However, when the present invention is applied to photoconductors in which the image does persist, the development may be continued after the exposure has been terminated, but an essential feature of the present invention is the application of development current effectively during the exposure. The object of the present invention is to permit visual control of the photoconductographic process. This eliminates the need for trial exposures or extensive computations.

According to the present invention the image (while it is being exposed and developed) is watched and the exposure is terminated when the image reaches a preselected density. This density may be exactly that which is desired in the final print, in which case the development is also terminated, or this density may be some lower value and the exposure is terminated but the development is allowed to continue. The image may be watched during this continued development and a second preselected density will then determine when the electric current causing the development should also be terminated.

The present invention has two essential features, one the manner in which the electric current is applied and the other the use of non-actinic illumination for examin ing of the image during development. The light from the actinic image itself is, of course, distributed imagewise, i.e. non-uniformly. It is better for visual examinat on of an image to have uniform illumination in addition to the imagewise radiation. So that this will not interfere with the image formation, this uniform illumination is selected to be non-actinic. For example zinc oxide in resin photoconductors which are commonly used are sensitive whine and ultraviolet light but unless they have been purposely sensitized to yellow and red wave lengths, they are not sensitive to the latter.

A photoconductographic sheet consists of a photoconductive layer in electrical contact (directly or through a 'unidimensional conducting layer) with a conducto-recording or electrosensitive layer, often referred to as an electrolyte. T he recording layer may be integral with or on a separate support from the photoconductive layer. In the commonest form of the present invention, the recording layer is an electrolyte liquid spread on the photoconductor immediately prior to exposure. It may be washed off after exposure and development, if desired. Sensitivity of the photoconductive layer to incident radiation, sensitivity of the recording layer to the 3 passage of electric current and the electric potential applied for development all affect the ultimate print density and contrast.

'In order to utilize the photosensitvity of the photoconductor most efiiciently, the processing should be done both during and (if the conductivity persists) following exposure. Development entirely subsequent to exposure does not utilize the maximum conductivity which occurs during exposure itself. Development which is cut off when the exposure is terminated, does not utilize the residual effect. Therefore least exposure is required when the development is to be both during and immediately following exposure.

In photoconductography a DC. electric current is applied by the electrodes and, when the development is performed during exposure, the front one of the electrodes is in the path of the light projected to form the image. Transparent electrodes have been proposed for this purpose. The present invention does not rely on the transparency of this electrode, however. The other electrode is in contact with the rear surface of the photo conductographic sheet and may be a metal plate or it may, during development of the image, move across the rear surface while the front electrode, described below, is moving across the front surface, with the electrodes directly opposite each other.

According to the present invention the front electrode is a narrow one either of metal or in the form of a brush or sponge. This electrode sweeps across the surface of the sheet with substantially uniform velocity during the exposure. This feature of the invention provides many advantages and objects. It permits the image to be seen during development and it provides a high current density without the necessity of a large source of potential, since the potential is applied only over a restricted area of image at any one moment. Except in the special case where this front electrode itself is made transparent, the area behind it is dark and development occurs primarily in this dark area or in the image area immediately adjacent thereto. If the conductivity cuts off immediately when the exposure is terminated, there would be no variations behind the electrode and hence the present invention is most useful with photoconductors in which the image effect persists at least momentarily after the exposure is cut off. It is also desirable to have somewhat longer persistence so that useful development may be continued after the exposure is terminated for the whole image.

Since the photoconducting layer of the photoconductographic sheet is preferably coated on a metal foil and is hence opaque, the exposure is normally made on the front surface thereof through a thin layer of electrolyte.

The sweeping action of the front electrode may be purely transverse by having a narrow roller or brush move back and forth, or successively in one direction, across the print, or it may be an angular sweeping such as that normally provided by automobile windshield wipers. When the angular system is used, it is preferable to have the electrode itself wedge shaped so that the leading and trailing edges thereof are radial with respect to the center of the rotation of the sweeping motion. This provides a uniform amount of development for all areas.

The simpler embodiments of the invention have a liquid electrolyte applied by a brush to the surface of the photoconductor. This may actually be applied after the exposure is started, but image formation can take place only after there is some electrolyte. The front electrode itself may be the brush which applies the electrolyte and the surface of the photoconductor is sensibly wet after the first stroke of such a brush. Actually a wet brush will contain in itself sufficient electrolyte for the development of several prints.

The image forming light is most intense in the areas which darken during development. The density and contrast thus produced is apparently reduced by the manner in which it is illuminated by the image forming light. According to the present invention uniform illumination is also provided, as discussed above so that the density image may be observed while it is being formed. The general illumination is non-actinic and may for example be provided by a yellow safelight. The image illumination may be by white light. An additional refinement, which is not absolutely essential but which eliminates all of the objectionable effects of the image forming light as far as the observer is concerned, consists of two filters in addition to the one in the safelight, for example a blue filter is placed in the image forming beam and a third filter, for example a yellow filter, is placed in front of the eye of the observer so that the observer sees only light from the general illumination (yellow safelight) and does not see any of the image forming light. The blue filter does not cut out any appreciable amount of the actinic light and hence does not appreciably increase the time of exposure.

The operation of the invention and its advantages will be fully understood from the following description when read in connection with the accompanying drawing in which:

FIG. 1 illustrates schematically in perspective a preferred embodiment of the present invention.

FIG. 2 illustrates an alternative arrangement of the easel, and processing mechanism used in FIG. 1.

In FIG. 1 a negative transparency 10 is illuminated by a lamp 11 which emits actinic radiation, and perhaps also some non-actinic radiation. A lens 12 forms an image 14 of the negative 10 on a photoconductive sheet. This sheet consists of a layer 15 of zinc oxide in resin coated on an aluminum foil 16 which is laminated to a paper support 17. The whole photoconductographic sheet is laid on a rigid easel 18 which is of insulating material in the example shown but which may be of metal if provision is made to insulate it from one side or the other or from bot-h sides, of the electrical development system. The surface of the photoconductor 15 is wet with an electrolyte which darkens upon the passage of current. This may be an electroplating system in which there is a cathodic deposit on the photoconductor 15 or it may be any of the other electrolytic systems discussed in the above mentioned copending applications, which provide a visual image.

A front electrode 20 which is wedge shaped and which moves with uniform velocity back and forth under the action of a windshield wiper motor 22 sweeps across the front surface of the photoconductographic sheet, and covers at least all of the area of the image 14. This electrode may be of metal or preferably may have a spongy surface and the electrolyte itself may be applied by this sweeping electrode. A source of DC. potential illustrated schematically at 23 is connected so that the aluminum foil layer 16 is negative and the windshield wiper electrode 20 is positive. Thus the photoconductive layer 15 acts as the cathode in the electrolytic bath. Closing the switch 24 causes the potential to be applied during the exposure and, if desired, to be continued after termination of the exposure. The DC potential may be applied in the other direction when the color formation is such that it occurs at the anode.

To permit the density formation to be observed visually according to the present invention, a safelight 25 provides yellow illumination which is non-actinic with respect to the photoconductor 15. An observer whose eye is indicated at 26 watches the formation of this image and terminates the exposure and possibly also the development, at the time the apparent image reaches a preselected value.

A special refinement adds filters 27 and 28. The filter 27 is yellow so that the light from the safelight 25, reflected by the photoconductor 15 is visible for observation. However. the filter 28 is blue so that it passes actinic light to form the image 14, but this light is not seen through the filter 27. The advantage of this added refinement arises from the fact that the image forming light is brightest where the density is the greatest and hence this image forming light tends to reduce the contrast of the image as it forms.

If the preselected value of image density at which the light 11 is turned off is that of the desired finished print, the switch 24 is also opened and the finished print is removed from between the electrodes. Alternatively the density at .the time the image projection is terminated may be preselected to have a value somewhat less than the ultimate value. The image may be then intensified by chemical means or the electrolytic development may be continued. That is the electrode 20 may continue to sweep across the image either to complete development at some preselected total time or under the visual control, until the image reaches the ultimate desired density value.

Of course the conductorecording layer of electrolyte may be a solid layer coated on the photoconductor, but the preferred forms of the invention simply have a thin layer of liquid applied by a brush.

In FIG. 2 the photoconductographic sheet is laid on an easel 30 across which a bar 31 moves transversely in grooves 32. The easel 30 is an insulator in the arrange ment shown. The bar 31 is of metal and carries a felt swab or brush 33 which is Wet prior to exposure and development and which is moved transversely, at uniform velocity back and forth across the image areas on the photoconductor 15. The brush 33 applies the electrolyte and acts as the moving electrode according to the invention. Again the DC. source of potential 23 applies negative potential to the aluminum foil 16 and positive potential to the bar 31. The felt 33 will hold sulficient electrolyte for the development of several prints. However, in the arrangement shown, it may be moved to the far end of the guide rails 32 and additional solution 41 in a container 40 may be brought up to wet the felt 33 immediately before the next processing step.

Roller type electrodes may also be used but the simple brushing action illustrated in FIGS. 1 and 2 is quite satisfactory.

Having thus described two embodiments of the invention, it is understood that the invention is not limited thereto but is of the scope of the appended claim.

Iclaim:

6 A photoconductographic process comprising the steps of:

projecting onto the front surface of a photoconductive zinc oxide in resin layer insensitive to at least some Wave lengths of visible radiation, an image in radiation which is actinic to said photoconductive layer,

passing substantially simultaneously with said projecting, electric current through the areas of the layer rendered conducting by said image and through an electrolyte in contact therewith, which electrolyte electrolytically deposits a visible material, said current being between electrodes, the rear one of which electrically contacts the rear surface of the layer and the front one of which electrically contacts the front surface of the layer partly through said electrolyte and is narrower than said image,

sweeping the front electrode with uniform velocity brushingly across the front surface of the layer several times during said projecting,

illuminating the layer substantially uniformly with nonactinic visible light for viewing,

continuing said projecting and sweeping until,

and terminating said projecting when, the electrolytic deposit on the layer reaches a preselected apparent density,

continuing said sweeping and passing of current after the terminating of the projecting,

and later terminating said sweeping and passing of current when the electrolytic deposit reaches a second preselected level of density.

References Cited by the Examiner UNITED STATES PATENTS 1,959,233 5/1934 Franke. 2,692,178 10/1954 Grandadam 961 2,963,335 12/1960 Hall et a1 96-1 X 3,010,883 11/1961 Johnson et a1 20418 FOREIGN PATENTS 151,971 5/ 1904 Germany.

WINSTON A. DOUGLAS, Primary Examiner.

PHILIP E. MANGAN, JOSEPH REBOLD, JOHN H.

MACK, Examiners.

I. E. ALIX, R. GOOCH, A. B. CURTIS,

Assistant Examiners. 

